Device and method for managing indoor air quality via filtration and dehumidification

ABSTRACT

A device and method are specified for managing indoor air quality. More particularly, to promote health, comfort, and air quality, a device and method are proposed for filtering and dehumidifying air in an indoor environment, e.g., air that flows through an HVAC system.

BACKGROUND OF THE INVENTION

This invention relates generally to managing indoor air quality,especially in connection with heating, ventilation, and air conditioning(HVAC) systems. More particularly, a device and method are proposed forfiltering and dehumidifying air in an enclosed (indoor) space—forexample, the air that flows through an HVAC system—so as to improveindoor air quality and promote health and comfort.

Managing indoor air quality is a well-established but continuallyevolving field of technology. Particularly in industrialized nations,populations have become largely “indoor societies,” with many peoplespending substantial portions of most days indoors. Millions of peoplework in homes or offices. Millions attend schools. Many senior citizensspend a majority of their day indoors. Many young children spend largeamounts of time indoors, whether at home or in other indoorenvironments.

Consequently, indoor air quality is an area of growing importance andconcern. The United States Environmental Protection Agency (EPA) hasidentified indoor air pollution as one of the top five seriousenvironmental health risks, and mold as a health threat of growingconcern within the indoor environment. “Most Americans do not have aclear sense of the significant health risks of indoor pollution. Theyalso do not know what they can do to reduce risk for asthma, cancer, andother serious diseases caused by indoor pollutant exposure.” See HealthyBuildings, Healthy People, EPA Document #402-K-01-003 (October 2001).

A variety of indoor air pollutants are known to exist. Some of theseinclude bioaerosols, dust mites, animal dander, volatile organiccompounds, carbon monoxide, mold, bacteria, viruses, fungi, etc. In somecircumstances and concentrations, air pollutants are capable ofproducing a variety of effects undesirable to humans. Certainenvironmental factors are known or suspected to play a role in eitherinhibiting or promoting the proliferation of such pollutants in anindoor setting. Regulating or compensating for such factors is known asenvironmental control or management of air quality.

Ventilation is a primary consideration in managing indoor air quality.Without ventilation, pollutants within a closed environment have littlemeans of escape and can become more concentrated over time. Appropriateventilation, then, can be an important step toward reducing indoor airpollution. Outside air may be introduced into an indoor air space,subject to whatever additional environmental control processes may be inuse.

Filtration of indoor air is another important component in maintainingacceptable air quality. Mechanical filtration systems are commonly ratedaccording to the size of airborne particulates they are capable ofremoving and their particulate arrestance percentage. The AmericanSociety of Heating, Refrigerating, and Air-Conditioning Engineers(ASHRAE) has promulgated a widely-used “Minimum Efficiency ReportingValue” (MERV) Standard 52.2 to quantify these filter performancecharacteristics. For example, commonly recommended air filtrationsystems for newer commercial and residential buildings might typicallycarry a rating around MERV 11, indicating a capability to removeparticles about 1 to 3 microns in diameter with an arrestance rate ofabout 95% or better. To remove even smaller particulates, a morediscriminating filter such as a High Efficiency Particulate Air (HEPA)filter with a rating at or near MERV 20 can be employed. To meet HEPAstandards, a filtration device must be able to capture at least 99.97%of all airborne particles 0.3 microns or more in diameter that enter it.

Irradiation may also offer certain environmental control benefits.Naturally occurring sunlight includes ultraviolet (UV) rays whichinhibit the growth of many microbes in out-of-doors environments.Artificial germicidal UV light can be similarly applied in indoor airquality management to inhibit the growth of bacteria, viruses, molds,etc. UV-C, the germicidal wavelength of UV light, can damage the nucleicacid of microorganisms by forming covalent bonds between certainadjacent bases in their DNA. The formation of such bonds prevents theDNA from being unzipped for replication, hindering the organism fromreproducing.

Proper humidity control is an important but often-overlookedconsideration in indoor air quality management. Various organisms,health concerns, and other reactions can increase or decrease with theindoor relative humidity level. See Criteria for Human Exposure toHumidity in Occupied Buildings, Dr. Elia Sterling (1985). “Biologicalair pollutants are found to some degree in every home, school, andworkplace.” “A number of factors allow biological agents to grow and bereleased into the air. Especially important is high relative humidity,which encourages house dust mite populations to increase and allowsfungal growth on damp surfaces.” See Indoor Air Pollution, EPA Document#402-R-94-007 (1994). The basic refrigeration process that allowsdehumidification of moisture-laden air has been known for sometime—i.e., compressing and condensing refrigerant gas and then allowingthis gas to evaporate in a controlled manner through some pressure-dropmetering device—but effectively integrating targeted dehumidificationinto the overall processes of indoor air quality management is notcommon at this time.

The basic process of refrigeration to achieve dehumidification can beunderstood by description of a typical implementation of this process. Asimple dehumidification system would typically include a refrigerantcompressor, an evaporative coil (a refrigerant-to-air heat exchanger,also known as a dehumidification coil), a condenser coil (anotherrefrigerant-to-air heat exchanger, also known as a reheat coil), arefrigerant metering device, assorted tubing connecting the systemcomponents so as to make a sealed or closed system, and an air blower orfan. The blower or fan operates in conjunction with the compressor andmoves air that is to be dehumidified through the system. Therefrigeration system, being closed, recycles the refrigerant throughseveral system components so that various changes of state are inducedto achieve the removal, addition, and conversion of energy in the formof latent and sensible heat.

In such a system the compressor receives superheated vapor andcompresses this vapor to a point beyond its condensing or liquefyingpoint, yet this compressed gas will not condense to a liquid statewithout the removal of heat; heat is removed as the gas moves throughthe condenser coil where the energy required to condense is exchangedwith the moving air stream. The liquid's temperature is further reduced(sub-cooled) before leaving the condenser. The sub-cooled liquid beingat relative high pressure in the system is passed through a meteringdevice (e.g., a valve, capillary tube, or other specialized orifice) tocreate a drop in pressure, allowing the refrigerant to change state andevaporate. The evaporation process requires energy (heat) to be addedback to the refrigerant, and this occurs in the evaporator coil. Thesource of the energy or heat is a stream of air moving through thesystem; because the evaporator is colder that the air stream, heat (bothsensible and latent) is removed from the air. The latent heat removalresults in water being removed from the air stream in the form ofliquid, typically referred to as condensate. Thus some dehumidificationof the air has been achieved. The gas—now super-heated beyond its pointof evaporation—is returned the compressor, where the cycle is thenrepeated.

Such a dehumidification process can be enhanced to higher operationalefficiency with the addition of an air-to-air heat exchanger (AXA) inthe system. With the addition of an AXA the ratio of sensible and latentheat removed can be adjusted. Increasing the latent heat removalcapacity allows for a greater volume of moisture removal in each systemcycle without the need to increase the overall operational capacity ofthe refrigeration system. The AXA pre-cools the incoming air streambefore the air enters the evaporator coil, and because of the air ispre-cooled the coil itself may typically operate at a lower temperatureso that it will be removing a greater amount of latent heat from theair. As a result more water will condense and be removed from the air.The air stream is then directed back through the AXA where it isreheated while serving as the source (“sink”) to cool the incoming airstream. In other aspects this high-efficiency dehumidification processoperates similarly to the basic process described before.

The present invention provides several novel combinations of some of theabove air quality management techniques, in a manner suited to achieveimproved performance over many existing environmental control systems.That the present invention is a distinct improvement over solutions inthe prior art will become more apparent from this specification.

SUMMARY OF THE INVENTION

To adequately handle the challenges of managing indoor air quality, morethan temperature must be addressed. Yet in the majority of airconditioned buildings today, temperature is the only air qualityvariable that is precisely monitored or regulated. Successfullycontrolling the sources of indoor air pollution must involve preciseregulation of at least humidity as well. Systems disclosing temperatureand/or humidity control are exemplified by such references as U.S. Pat.No. 5,598,715, issued Feb. 4, 1997, to Edmisten; U.S. Pat. No.5,088,295, issued Feb. 18, 1992, to Shapiro-Baruch; and U.S. Pat. No.2,255,292, issued Sep. 9, 1941, to Lincoln.

Humidity control is a basic building block of the present invention.Humidity that is too low can promote proliferation of some indoorpollutants such as ozone and certain bacteria and viruses. At extremelylow humidity levels, incidence of respiratory infections tends to rise.On the other hand, humidity that is too high can promote proliferationof many indoor pollutants as well, including fungi, dust mites, andcertain bacteria and viruses. Humidity control to improve overall indoorair quality thus becomes something of a balancing act of avoidingrelative humidity extremes at either end of the range. Current data andexperience suggest that an optimally balanced indoor humidity level formany environments may fall in the area of 40% to 60% relative humidity.Adjusting this range in either direction may be desirable in someapplications, e.g., where certain specific pollutants are considered tobe of greater significance and concern than others. Dehumidificationaspects of the invention are further described below.

In addition to temperature and humidity control, air should be filteredand circulated to remove airborne particulate matter, and fresh outsideair may be introduced to dilute concentrations of volatile organiccompounds. Other treatments such as irradiation may be employed as well.The present invention addresses some of these important indoor airquality control factors, resulting in improved indoor air quality andfurther resulting in potential health and comfort benefits.

Filtration alone will not achieve the full air quality benefits of thepresent invention, yet filtration remains an important component of theoverall device and method. Filtration can remove airborne particulatematter and thus help improve air quality. Particulate matter comprisesvery small particles of solids or liquids that vary in size, chemicalcomposition, and source. Such particles can remain suspended in air forlong periods of time; the smaller a particle, the longer it may remainairborne. When inhaled, some fine particles may be deposited in thelower respiratory tract and the gas-exchanging portions of the lung, andcan damage respiratory airways.

While various approaches to air filtration exist, certain preferredembodiments of the invention employ one or more mechanical filtrationstages including, e.g., a HEPA filter. Another preferred embodimentincludes a rubberized gasket around at least one mechanical filter, toform a tight seal inside the system and ensure that air passes throughthe filter and not around it. In still another embodiment, a systemcontrol device incorporating a humidistat will monitor and regulateenvironmental humidity and may also include an indicator to indicatewhen a mechanical filter or other expendable system components should bechanged.

To achieve suitable ventilation, fresh outside air may be introducedinto the indoor air space in a variation of the invention. Preferablythe outside air enters the system via a path that allows it to be atleast partially filtered and dehumidified before entering theconditioned indoor airspace. Incorporating such ventilation into theprocess or system of the invention can be a significant step inimproving the quality of indoor air, by diluting accumulated indoorpollutants.

Germicidal irradiation is implemented in a further optional embodimentof the invention. An embodiment employs a lamp producing UV light on theorder of 265 nanometers, which is considered a wavelength lethal to manyairborne microorganisms such as bacteria, viruses, and molds. Wavelengthand other lamp characteristics may be modified in accordance with theneeds of particular applications. The lamp preferably is positioned soas to expose the evaporator, drain pan, and condensate water togermicidal UV light radiation. Airflow may also be subjected to theradiation. Various safety and convenience features may be included withthe UV lamp, such as a lamp shutoff switch, a sight glass for safe andeasy lamp inspection, and a protective cover with a safety interlockswitch to deactivate the lamp before a person can access or service thedevice. Preferably the UV lamp is constructed to high quality standardsto achieve suitable performance and reliability, including the use ofhard glass tubing adapted to optimize UV transmittance levels.

In most variations of the device of the invention, an advancedcombination of environmental control techniques is implemented inconnection with a separate HVAC system. This can be achieved, forexample, by integrating the environmental control solutions into amodule that can be relatively easily installed in interface with anexisting HVAC system to enhance its operation and utilize its airdistribution system (e.g., fans, vents, and ductwork). A commoninstallation configuration places the module in parallel with anexisting HVAC airflow path, and may utilize a blower and/or damper todirect airflow through the module at appropriate times. The module maybe arranged in a horizontal, vertical, or other configuration as needsmay dictate. Enhancement of process control may be achieved through theuse of dampers and by providing electrical blower interlock with anexisting HVAC system blower. A similar module may be installed somewherewithin an indoor air space, for example in a stand-alone configuration.

Embodiments of the device and method of the invention trigger anenvironmental control process at a suitable time (e.g., when ahumidistat or other feedback mechanism senses environmental conditionsoutside some preselected range). HVAC airflow optionally is at least inpart diverted so as to be subjected to aspects of the process. HVACairflow (together with fresh outside airflow, in some embodiments) isdirected through a filtration process for removing airborne particulatematter. Dehumidification is achieved as airflow is directed throughstages of an AXA that first cause flowing air to give up some sensibleheat, reducing air temperature so that it approaches the dew point. (Insome conditions dew point may be reached in the AXA and moisture maycondense, a condition which should preferably be accommodated by thedevice's design, e.g., by appropriate placement of a drain pan.) The airthen passes through the first of two refrigeration heat exchanger coils,which preferably operates just above the freezing point to achieveprimarily moisture condensation or latent heat removal. The air exits ata low temperature and passes over an irradiating UV lamp, if applicable,then passes through a second stage of the AXA, where it begins areheating process. Once exiting the AXA, the air is directed through asecond refrigeration heat exchanger where it is reheated and the excessheat of refrigeration is added. The air is pulled through a blower andreintroduced (as cleaner, dehumidified air) through the HVAC system tothe climate-controlled indoor space. The cycle is continued until adesired humidity level is achieved.

The invention and some of its variations may be more fully understoodwith reference to the accompanying drawings.

DRAWINGS REFLECTING SOME EMBODIMENTS

FIG. 1 is a side sectional view of a module embodying at least part of adevice of the invention, depicted in a horizontal configuration,indicating with arrows a typical airflow.

FIG. 2A is a perspective view of a module embodying at least part of adevice of the invention, depicted in a vertical configuration.

FIG. 2B is a front sectional view of the same embodiment as FIG. 2A.

FIG. 2C is a side sectional view of the same embodiment as FIGS. 2A &2B.

FIG. 2D is an input end view of the embodiment in FIG. 2E.

FIG. 2E is a side sectional view of a horizontally configured embodimentthat is essentially the same as FIG. 1, without arrows depictingairflow.

FIG. 2F is an output end view of the embodiment in FIG. 2E.

FIG. 3 is a simplified side view of an embodiment of the invention as inFIGS. 1 & 2E, installed in connection with an existing HVAC ductworksystem.

FIG. 4 is a simplified side view of an embodiment of the invention as inFIGS. 1 & 2E, installed partially in connection with an existing HVACductwork system, and shown with outside air outside air ventilation andcrawl space options.

FIG. 5 is a simplified side view of an embodiment of the invention as inFIGS. 1 & 2E, installed partially in connection with an existing HVACductwork system, and shown with outside air ventilation and crawl spaceoptions. Also shown is added ductwork for a dedicated airflow returnpath.

FIG. 6 is a flowchart depicting a method in accordance with theinvention.

DESCRIPTION OF SOME EMBODIMENTS

With reference to the drawings, it will be seen that a basic embodimentof the device of the invention consists of a closed refrigeration systemincluding a compressor, dehumidification coil (evaporator), reheat coil(condenser), refrigerant metering device, associated tubing connectingthese components (typically copper), and a drain pan (e.g., of stainlesssteel). Some of the smaller and standardized elements of the system arenot labeled in the drawings or given special attention in the discussionof the drawings, such elements being well known in the arts ofrefrigeration and HVAC engineering. Further aspects of the device of theinvention may include a blower, an air-to-air heat exchanger, apre-filter, a main HEPA filter, and a germicidal UV lamp.

FIGS. 1 and 2E illustrate a basic embodiment of the device of theinvention, shown in a horizontal configuration. FIGS. 2D and 2F showopposite end views of the same embodiment.

FIGS. 2A, 2B, and 2C illustrate a functionally similar embodiment of thedevice of the invention, but in a vertical rather than horizontalconfiguration. Element labeling numbers for this alternate configurationwill be mentioned below in parentheses. See, e.g., blower 190 (290).

The functionality of the elements of these embodiments will be discussedwith reference to an airflow passing through the device. Airflow 10originates in the environment for which air quality is to be regulated,and enters module 100 (200) at intake opening 110 (210). Externalairflow 5 (from outside ventilation) can optionally be combined withairflow 10. In a preferred embodiment providing more than one filtrationstep, the airflow 10 (together with external airflow 5, if applicable)passes first through a high-efficiency pre-filter 120 (220) to removelarger airborne particles, and then through a main HEPA filter 130 (230)to remove smaller airborne particles. Various filtration devices couldbe used interchangeably in the invention, but the configurationillustrated here is a presently preferred embodiment.

Having passed through the filtration devices, airflow 10 is now depictedas filtered airflow 20. Filtered airflow 20 enters an air-to-air heatexchanger 140 (240) and is cooled. Cooled airflow 30 passes across thedehumidification coil/evaporator 150 (250) so that moisture will beremoved from the air. In a well-known refrigeration process, refrigerantcontained within the system is compressed in compressor 170 (270) andmetered through evaporator 150 (250). Moisture from the airflow 30 thuscondenses and collects by the operation of gravity in a drain pan 160(260), which is preferably constructed of stainless steel or anothernon-corrosive material. UV lamp 165 optionally irradiates the airflowpassing by, as well as the drain pan and the liquid collected in it,tending to destroy certain pollutants that might otherwise collect orpass through.

The dehumidified airflow 40 returns through the AXA 140 (240) asdescribed above, being warmed by and in turn cooling airflow 20. Thewarmed, dehumidified airflow 50 then passes through the reheatcoil/condenser 180 (280) where heat is transferred from compressedrefrigerant in the condensor 180 (280) to the airflow 50 and it passeson as airflow 60. Blower 190 (290), which serves to actuate the airflowsthrough the overall system, now forces the dehumidified air 60 backtoward the indoor environment for which the air quality is beingregulated (e.g., by way of ductwork). Electrical controls for theoverall system are centralized in control box 185 (285). Other controlelements not depicted in the drawings could include a humidistat andother remote sensors and controls, which typically would be inelectrical communication with control box 185 (285).

FIG. 3 illustrates how the module 100 (200) can be integrated intoexisting HVAC ductwork. In a typical HVAC system installation, returnduct 300 carries air from the controlled environment back to an airhandler, furnace, or similar equipment (not shown). When a deviceaccording to the invention is integrated into such a system, air ductmaterial is used to construct a diversion path 310 to carry a portion ofthe HVAC system return airflow through module 100, and after thisdiverted airflow has been filtered and dehumidified in module 100 it isreturned to the HVAC system return duct 300 by way of insertion path320.

FIG. 4 elaborates on the illustration of FIG. 3 by showing someadditional optional features for integrating the invention into anexisting HVAC system. The primary additional feature in this embodimentis the provision of an outside air ventilation input to the system.Intake hood 330 (preferably screened) is provided outside the structureof the environment to admit fresh outside air into the system. Outsideair path 332 is constructed to carry this air into the system. Manualdamper 334 allows for closing the air flow when necessary. Optionalpower damper 336 can be integrated into the system control set. Thus,outside air enters through hood 330, passes through path 332 and pastdamper(s) 334, 336 (when open), into module 100, to be mixed with indoorair for filtration and dehumidification. Another feature hereillustrated is an optional partial air return of dehumidified air to anarea such as a crawl space or unconditioned basement. Path 342 diverts afraction of the output airflow from module 100, carrying some air pastmanual damper 344 and backflow damper 346 (when these are open) into theunconditioned space 340.

FIG. 5 represents an additional variation in which for whatever reason aseparate input airflow path into module 100 is needed, rather than adiversion from existing HVAC ductwork 300. Here, a dedicated air return350 is added, which carries air from the conditioned space to low intakeof module 100. The filtered, dehumidified air is then sent back towardthe conditioned environment through insertion path 320 via ductwork 300.

Many modifications or expansions upon the invention itself and thevarious illustrative embodiments herein described still fall within thespirit and scope of the invention, and should be so considered.

1. In an environment supplied by an airflow, a method comprising:Determining a satisfactory level of an environmental humidity;Monitoring said environmental humidity; So long as said environmentalhumidity exceeds said satisfactory level: continuously filtering saidairflow to remove particulate matter therefrom, and continuouslydehumidifying said airflow to remove moisture therefrom; When saidenvironmental humidity reaches a satisfactory level, ceasing tocontinuously filter and dehumidify said airflow.
 2. A method accordingto claim 1, wherein said dehumidifying comprises: causing said airflowto pass a first time through an air-to-air heat exchanger to lower thetemperature of said airflow; causing said airflow to pass through anevaporative dehumidification coil stage to remove moisture from saidairflow; causing said airflow to pass a second time through saidair-to-air heat exchanger to raise the temperature of said airflow; andcausing said airflow to pass through a condensing reheat coil stage. 3.A method according to claim 2, further comprising adding to said airflowa supply of air from outside said environment.
 4. A method according toclaim 3, further comprising irradiating said airflow.
 5. A methodaccording to claim 4, wherein said filtering comprises: causing saidairflow to pass through a pre-filtering stage to remove largerparticulate matter therefrom; causing said airflow to pass through afine-filtering stage to remove smaller particulate matter therefrom;removing from said airflow at least about 99.97% of all particulatematter greater than about 0.3 microns in diameter.
 6. A method accordingto claim 1, wherein said filtering comprises: causing said airflow topass through a pre-filtering stage to remove larger particulate mattertherefrom; causing said airflow to pass through a fine-filtering stageto remove smaller particulate matter therefrom; removing from saidairflow at least about 99.97% of all particulate matter greater thanabout 0.3 microns in diameter.
 7. A method according to claim 6, whereinsaid dehumidifying comprises: causing said airflow to pass a first timethrough an air-to-air heat exchanger to lower the temperature of saidairflow; causing said airflow to pass through an evaporativedehumidification coil stage to remove moisture from said airflow;causing said airflow to pass a second time through said air-to-air heatexchanger to raise the temperature of said airflow; and causing saidairflow to pass through a condensing reheat coil stage.
 8. A methodaccording to claim 6, further comprising adding to said airflow a supplyof air from outside said environment.
 9. A method according to claim 6,further comprising irradiating said airflow.
 10. A method according toclaim 7, further comprising adding to said airflow a supply of air fromoutside said environment.
 11. For an environment, a device comprising: Ablower to divert an airflow from said environment and cause said airflowto pass through said device; An intake stage for receiving said airflowinto said device; A filtration stage coupled to said airflow intakestage; A dehumidification stage coupled to said filtration stage; Anoutput stage for returning said airflow to said environment; A controlstage for monitoring at least one characteristic of said environment andfor regulating operation of said device.
 12. A device according to claim11, wherein said dehumidification stage comprises an air-to-air heatexchanger for pre-cooling said airflow; a compressor for compressing arefrigerant; a dehumidification coil for removing moisture from saidairflow; and a reheat coil.
 13. A device according to claim 12, whereinsaid filtration stage comprises a pre-filter for removing largerparticulate matter from said airflow and a fine filter for removingsmaller particulate matter from said airflow.
 14. A device according toclaim 13, wherein said intake stage comprises means for receiving asupplemental airflow from outside said environment and combining saidsupplemental airflow with said airflow received from said environment.15. A device according to claim 14, further comprising an ultravioletlamp for irradiating said airflow and at least a part of said device.16. For an environment to which a duct network is connected, a devicecomprising: A blower to divert an airflow from said duct network andcause said airflow to pass through said device; An intake stage forreceiving said airflow into said device; A filtration stage coupled tosaid airflow intake stage; A dehumidification stage coupled to saidfiltration stage; An output stage for returning said airflow to saidduct network; A control stage for monitoring at least one characteristicof said environment and for regulating operation of said device.
 17. Adevice according to claim 16, wherein said filtration stage comprises apre-filter for removing larger particulate matter from said airflow anda fine filter for removing smaller particulate matter from said airflow.18. A device according to claim 17, further comprising an ultravioletlamp for irradiating said airflow and at least a part of said device.19. A device according to claim 18, wherein said intake stage comprisesmeans for receiving a supplemental airflow from outside said environmentand said ductwork, and combining said supplemental airflow with saidairflow received from said ductwork.
 20. A device according to claim 19,wherein said dehumidification stage comprises an air-to-air heatexchanger for pre-cooling said airflow; a compressor for compressing arefrigerant; a dehumidification coil for removing moisture from saidairflow; and a reheat coil.